Seat back inertia latch systems such as disclosed in our prior U.S. pat. applications Ser. No. 945,303 filed Sept. 25, 1978 now U.S. Pat. No. 4,223,946, Ser. No. 06/047,362 filed June 11, 1979 now and U.S. Pat. Ser. No. 06/090,343 filed Nov. 1, 1979 employ inertia elements having backward extensions positioning the inertia element in an engagement oriented relationship with the latch element when the seat back is in normal position which overcomes the gravity biasing of such inertia element toward a release position. Disengagement of each such extension with a stationary element of the seat is progressively effected by initial seat back tilting in a forward direction to permit gravity release of the inertia element from its latching orientation. Such backward extension of the inertia element per se together with the cooperating stationary back stop project to some extent into the available space fo the rear passenger. Such extension and back stop also involve some weight and material costs which potentially can be saved if eliminated. In addition tolerance requirements inherently involve some clearance between the inertia and latching element, together with some inertia element movement upon sudden deceleration, in order to reach full latch engagement orientation which to some extent inhibits latching efficiency.